gpio: add userspace ABI for GPIO line information

This adds a GPIO line ABI for getting name, label and a few select
flags from the kernel.

This hides the kernel internals and only tells userspace what it
may need to know: the different in-kernel consumers are masked
behind the flag "kernel" and that is all userspace needs to know.

However electric characteristics like active low, open drain etc
are reflected to userspace, as this is important information.

We provide information on all lines on all chips, later on we will
likely add a flag for the chardev consumer so we can filter and
display only the lines userspace actually uses in e.g. lsgpio,
but then we first need an ABI for userspace to grab and use
(get/set/select direction) a GPIO line.

Sample output from "lsgpio" on ux500:

GPIO chip: gpiochip7, "8011e000.gpio", 32 GPIO lines
        line 0: unnamed unlabeled
        line 1: unnamed unlabeled
(...)
        line 25: unnamed "SFH7741 Proximity Sensor" [kernel output open-drain]
        line 26: unnamed unlabeled
(...)

Tested-by: Michael Welling <mwelling@ieee.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
index 3f93e1bcd3dd..416ce47f2291 100644
--- a/include/uapi/linux/gpio.h
+++ b/include/uapi/linux/gpio.h
@@ -25,6 +25,32 @@ struct gpiochip_info {
 	__u32 lines;
 };
 
+/* Line is in use by the kernel */
+#define GPIOLINE_FLAG_KERNEL		(1UL << 0)
+#define GPIOLINE_FLAG_IS_OUT		(1UL << 1)
+#define GPIOLINE_FLAG_ACTIVE_LOW	(1UL << 2)
+#define GPIOLINE_FLAG_OPEN_DRAIN	(1UL << 3)
+#define GPIOLINE_FLAG_OPEN_SOURCE	(1UL << 4)
+
+/**
+ * struct gpioline_info - Information about a certain GPIO line
+ * @line_offset: the local offset on this GPIO device, fill in when
+ * requesting information from the kernel
+ * @flags: various flags for this line
+ * @name: the name of this GPIO line
+ * @label: a functional name for this GPIO line
+ * @kernel: this GPIO is in use by the kernel
+ * @out: this GPIO is an output line (false means it is an input)
+ * @active_low: this GPIO is active low
+ */
+struct gpioline_info {
+	__u32 line_offset;
+	__u32 flags;
+	char name[32];
+	char label[32];
+};
+
 #define GPIO_GET_CHIPINFO_IOCTL _IOR('o', 0x01, struct gpiochip_info)
+#define GPIO_GET_LINEINFO_IOCTL _IOWR('o', 0x02, struct gpioline_info)
 
 #endif /* _UAPI_GPIO_H_ */